Magnetron power supply circuits



2 Sheets-Sheet 1 March 1951 w. c. BROWN ET AL MAGNETRON POWER SUPPLYCIRCUITS Filed March 11, 1947 March 6, 1951 w. c. BROWN EIAL 2,543,887

MAGNETRON POWER SUPPLY CIRCUITS Filed March 11, 1947 2 Sheets-Sheet 2/NvE/v7v/2s W/LL/AM C. BROWN JOHN E. STACY zii v Patented Mar. 6, 1951UNITED STATES PATENT OFFICE MAGNETRON POWER SUPPLY CIRCUICIJS William C.Brown, Lincoln, and John E. Stacy,

Winthrop,Mass., .assignors to Raytheon 'Manufacturing Company,Newton,.Mass., a corporation of Delaware ApplicationMarch 11, 1947.,Serial No. 738,840

An object of this invention is to devise circuits for operating aplurality of -magnetrons, whereby an increase in overall efiiciency ofoperation may be obtained.

Another object is to provide circuits by the use of which magnetrons maybe operated directly from an alternating current source, without thenecessity of using therewith a separate rectifier power supply.

A further object is to devise circuits for operating magnetron or a pairof magnetrons from an alternating current source in a self-rectifyingmanner.

A still further object is to devise magnetron circuits which provide aself-regulating action, whereby no external voltage regulators arerequired.

An additional object is to devise magnetron-circuits wherein themagnetron anode current is utilized as a source of excitation for theelectromagnet which provides the magnetic field for the magnetron.

Still another object is to devise magnetron circuits wherein the meansused for producing :the magnetic field for the magnetron has additionalfunctions.

The foregoing and other objects of the-inven tion will be bestunderstood from the following description of some exemplificationsthereoflreference being had to the accompanying drawings, wherein:

Fig. 1 is a set of curves useful in explaining the operation of theinvention; and

Figs. 2, 3, and 4 are diagrammatic representations of different circuitarrangements according to the invention.

Now referring to Fig. l, a family of representative anode voltage-anodecurrent (E11 vs. 1p) curves A, B, C, and D are shown for anelectrondischarge device of the magnetron type. Each of the curves A, B,C, and D is drawn for a single constant value of magnetic intensity inthe magnetron, these values of magnetic intensity increasing from thelowermost curve A to the uppermost curve D. As will be noted, curves A,B, C, and D are substantially parallel to each other, and each curve issubstantially linear and has a very small slope throughout the greaterportion of its length.

i It is very often desirable to operate magnetrons directly from asource of alternating current,

.11 Claims. ((1250-27) 2 rather than operating them from a separateauxiliary power supply as isconventionally done) in order to eliminatethe rectifier power supply together with the losses naturally .presenttherein. It is desirable, of .course, to reduce total system losses inorder to raise the overall efiiciency of the system.

If, now, the sinusoidal alternating anode supply voltage represented bycurve F is applied to characteristic curve D, -no plate current willflow in the magnetron until voltage F reaches a value .a,-a't whichcurveD intersects the axis of-zeroi since a voltage of this value isrequired to overcome the current-cutoff effect of the magnetic field. AsvoltageF reachesand passes valuea, the magnetron plate current G willstart from zero and will increase rapidly, because of the very smallslope of characteristic curve D. The magnetron plate current G increasesas .pl'ate voltage F increases, until voltage F reaches its maximum orpeak value b. At this peak voltage value, a value c of plate currentflows in the magnetron, this value being quite 'large'as shown, due tothe small slope of characteristic D. As the magnetron plate voltage vFdecreases from its peak value'b, the magnetron plate current G alsodecreases rapidly from its maximum value 0, until voltage value-aisreached .in the-downward swing of voltage F, at which time themagnetron plate current "G is again zero, as determined bycharacteristic D.

The time interval t1, between the instant at which voltage rF' reachesvalue a in its upward swing and. the instant-at which said voltage againreaches value a in its downward swing, :is quite smallas compared'to thetime t3 of a .full halfcycle of voltage F,-as is apparent from the drawing, since value a is'wel' l up on the upward swing of voltage F.Therefore, during the half--cycle of voltage 'F in which the magnetronanode is positive with respect to its cathode, only a very short steephigh-amplitude'pulse- G-of plate cur-'- rent will flow. Of course, sincea magnetron is an asymmetrical device or rectifier, :no platecurrentwill flow during the next half-cycle of voltage F, in which themagnetron-anode is negative with respect to its cathode.

Since the total length tr of the pulse of anode current is smallcompared to the time is of a half cycle of anode voltage, the powerfactor of the tube load is rather low and, also, since the inputtransformer is loaded only over a relatively small a magnetron in whichthe magnetic intensity remains constant during operation thereof, thisconstant magnetic intensitybeing supplied by a permanent magnet, forexample.

Pursuant to this invention it has been-found that, if the magnetroncurrent is used as .a.

tron plate current J swings downwardly toward the zero axis asdetermined by characteristic I-IH, this downward swing of the currentagain being substantially sinusoidal because of the fact thatcharacteristic H--H' is substantially linear as above described. Platecurrent J continues to decrease as the plate voltage F decreases, untilat the time when the supply voltage F is zero, the plate current J isalso zero.

It will be apparent, from the above analysis, that under theseconditions the magnetron acts as a pure resistance load across thealternating current source, and plate current J flows in a substantiallysinusoidal manner throughout the entiretime is of a half-cycle of sourcevoltage F,

As stated above, the peak value d of the mag- .netron plate current J(in the series electrosource of excitation for an electromagnet which"provides themagnetic field for the magnetron, the above-describeddisadvantages may be eliminated and the magnetron maybe operated veryefficiently from a source of alternating current.

v Where the magnetic field of the magnetron is supplied by the magnetronplate current, it has been found that the operating line or Ep-Ipcharacteristic of the magnetron is substantially as represented by curveH'H, which, as will be seen, passes through the origin, is curved onlyvery slightly over its'length and which has a substantial slope over itsentire length.

If the magnetic field of the magnetron is supplied'by the plate current,when there is no plate current there will be no magnetic field, andthere is nothing to prevent the increase of plate current from zero assoon as the plate voltage becomes greater than zero because there isthen no'magnetic field to produce a current-cutoff effect. Of course, asthe plate current increases, the magnetic field intensity alsoincreases, which 'might tend to cause the plate current to decrease, butthis does not happen because the plate voltage has also increased tocause an increased plate current. Therefore, characteristic H'H extendsapproximately asshown. This character- 'istic goes substantially throughthe origin as shown-because the hysteresis loop of the material of whichthe electromagnet core is made is very narrow.

v! If, 'now, the sinusoidal alternating anode supply voltage F isapplied to the magnetron under these conditions (with the plate .currentflowing in series through the electromagnet) the operating line in thiscase will be HH, as stated above, so that magnetron plate current(represented by curve J) will begin flowing as soon as the voltage Frisesabove zero. The plate current J will rise as the voltage rises, asdetermined by. characteristic Since characteristic H'-H issubstantiallylinear, the rise of plate current J will be substantiallysinusoidal. Characteristic H'-H is substantially linear and goes throughthe origin, so that in effect the magnetron under these conditions actssubstantially as a pure resistance load across the alternating currentsource. The magnetron plate current J continues to increase as the platevoltage F increases, until voltage'F reaches its maximum or peak valueb. At this peak'voltage value, a va ue d of plate current flows, thiscurrent value being determined from characteristic H. It will be notedthat value (I is substantially less than value c. v

s As voltage F begins its downward swing toward the aero axisfr'om it"speak'val'u'e b, the magnemagnet arrangement of the second case) issubstantially less than the peak value c of the magnetron plate currentG (in the permanent magnet arrangement of the first case). Since theplate current J in the second case flows over the entire half-cycle timeis, which time is substantially in excess of the time 151 over which theplate current G flows in the first case, for the same average power inthe two cases the peak current 01 in the second case can besubstantially less than the peak current 0 in the first case. Thisdecrease of the peak magnetron plate current is advantageous because ittends to lengthen the effective life of magnetron devices.

Since the plate current J in the second case fiows over the entirehalf-cycle time its, the input transformer secondary is loaded over thisentire half-cycle, thus efiectively raising the efficiency of operationof said transformer. Also, from a comparison of curves G and J, it canbe seen that curve J is substantially sinusoidal, whereas curve G isnot, and also that curve J extends throughout the entire half-cycle,whereas curve G extends over only a relatively small portion of saidhalf-cycle of supply voltage F. Therefore, the power factor in thesecond case (curve J) is substantially better than in the first case(curve G). Of course, it is desirable to keep the power factor of anyalternating current load as high as possible.

'For'reasons which will be explained hereinafter, it is desirable oreven preferable to provide a constant direct magnetic flux or biasthrough the electromagnet core, this fiux being in series aidingrelationship with that produced by the pulsating direct anode current ofthe magnetron flowing in series through the electromagnet exciting coil.Therefore, when the anode current goes to zero, there will still bemagnetic flux through the magnetron as a result of this bias. so thatthe lower end of solid line curve H does not go through the origin, butslopes ofi as shown. Characteristic H is curved only very slightly overthe major portion of its length and has a substantial slope over themajor portion of its length. As will be seen, the solid linecharacteristic H differs somewhat from the characteristic HH in thelower portion thereof.

With characteristic H, the sinusoidal supply voltage F must rise to thevalue e before any plate current (represented by curve K) flows. since avoltage of this value is required to overcome the current cutoff efiectof the biasing magnetic field. As voltage F rises beyond value c,magnetron plate current K increases from zero, rising approximatelysinusoidally to the same value d as before, this value being determinedby peak voltage value b and characteristic curve H. As voltage F swingsdownwardly, current K does also, the magnetron anode current falling tozero at the instant-when voltage F reaches value e in its downwardswing. Since value c is reached by voltage F-rather earily in the upwardswing thereof and rather late in the downward swing thereof, the time tzduring which plate current K flows is only very slightly .less than thehalf-cycle time ts. Therefore, thetime interval t2is-substantiallygreater than .the time interval ii of the pulse (3rwhich flows when no electromagnet is used, sothat the .power'factor inthis third case is still very much better than in the first case. Again,the peak current (1 can be substantially less than the peak current 0for the same average power, because the plate current K flows over amuch longer period of time than does plate current G. Also, with curve.K the input transformer is loaded over a much greater portion of thehalf-cycle than is the case with curve G.

Since the greater portion of characteristic curve H is substantiallylinear, the greater portion of anode current curve K is substantiallysinusoidal, so that the magnetron again acts as as a resistive loadacross the alternating current source, thus enabling a rather high powerfactor to be achieved.

In this third case, in which a direct'constant magnetic bias is usedalong with a plate-currentexcited electromagnetic, field, it is truethat the portion of the supply voltage curve F between zero and valuev eis in effect lost as far as the magnetron load is concerned. However,the voltage is relatively low in this region, so that only anunimportant proportion of the totalavailable volt-amperes is lost. Also,magnetrons will not ordinarily function to produce'a'radimfrequenoyoutput in this region of, very low anode voltage anyway, so that thereis no loss of radio-frequency power in so far as the radio-frequencyload is concerned. 'In addition, the envelope of a magnetron isordinarily made of a highly conductive material, such as copper, and themagnetic flux for the magnetron passes through and links with thisenvelope; it is desirable to limit the change of magnetic flux linkinwith this envelope so as to prevent an unduly high voltage being inducedtherein by transformer-action with the envelope acting as ashort-circuited secondary winding; therefore the magnetic flux should be:kept from going completely to ,zero at any time. For the above reasons,it is desirable to use a direct magnetic bias along with a seriesplate-current-excited electromagneticfield as the magnetic field for themagnetron.

Although the above description of magnetron operation with aplate-current-excited electromagnetic field has been made with referenceto a single magnetron connected across an alternatin current source, ithas. been found that it is ordinarily preferable to utilize apair ofmagnetrons connected in push-pull or as a full-wave rectifier across asource of alternating current, the magnetrons themselves providing theonly load across saidsource, and said magnetrons act.- ing as their ownpower supplies. In this case, the above analylsis still holds, so thatan anode current wave such as K will be produced in the appropriate oneof the pair of magnetrons during each successive half-cycle of theysource volt- ;age F. The advantages described'in detail. above Itrons.utilizev platercurrentz-excited electro-magnets for their magneticfields. of this invention are obtained, as discussed above,

The advantages by using the magnetron anode current as a source ofexcitation for the .electromagnet which furfnishes the magnetic fieldfor the magnetron.

By the utilization of magnetron anode current to excite the .magnetronelectromagnet, the magnetron anode current is held substantiallyconstant, regardless of line voltage variations,

as represented by curve M. Under these conditions, the anode currentwill have a peak value g which, as can be seen, is very much lower thanvalue I. Similar reasoning applies to increases in line voltage.Therefore, there are ordinarily extremely wide variations of anodecurrent with small difierences in applied anode potential in amagnetron. As a result, in order to maintain the desired substantiallyconstant power input to the magnetron, regardless of variations in linevoltage, very v ensitive voltage-regulating devices are ordinarilyrequired.

Now, utilizing this invention, the operating characteristic of themagnetron is again, as before, represented by curve H. With the appliedanode voltage L, from curve H it may be seen that the anodecurrent'utilizing the invention has a peak value 'h. Now, if the appliedanode voltage changes to curve M, the anode current will have a peakvalue 7'. As can be seen, due to the large slope of characteristic H,there is very little difference between values it and 7'. Similarreasoning applies to increases in line voltage. Therefore, by means ofour invention, without the use of any external or additionalvoltage-regulating devices, the magnetron plate current is stabilized ormaintained substantially constant regardless of variations in linevoltage, so that the desired substantially constant power input to themagnetron is maintained regardless of such variations.

It will be seen, from all of the above, that pursuant to this invention,there have been devised magnetron arrangements, using the magnetronanode current as a source of excitation for thev magnetronelectromagnet, in which no rectifiers are. necessary for operation ofthe magnetron or magnetrons, and in which no permanent magnets arenecessary. In this in- .vention, the. means for providing the magneticfield, which field is required in every magnetron, functions also, as.above described, to reduce the anode peak current while maintaining thesame average power, to increase substantially the length of the anodecurrent pulse, to raise the power factor of the magnetron load, toincrease the input transformer efficiency, and to maintain the magnetroncurrent substantially constant regardless of line voltage variations.

Figs. 2-4 represent, diagrammatically, three different circuitarrangements whereby the invention may be carried out. Referring now toFig. 2, the numerals I and .2 generally designate electronedischargedevices. of the. magnetron 2,54aes7 type, each including, for example,an evacuated envelope 3 made of highly conductive material, such ascopper, and provided with a plurality of inwardly-directed,radially-disposed anode vanes l. l 'he arrangement is such that eachpair of adjacent anode vanes 4 forms, together with that portion of theenvelope 3 lying therebetween, a cavity resonator whose natural resonantfrequency .is, as is well known to those skilled in the art, a functionof the geometry of the physical elements making up the same.

Centrally located in each envelope 3 is a highly electron-emissivecathode member 5, for example of the well-known alkaline-earthmetaloxide type, said cathode member being provided with conventionalmeans (not shown) for raising the temperature thereof to a levelsufficient for thermionic emission. v

An electromagnet, designated generally by 6,

may consist of a three legged soft iron core structure having airgaps inthe two outer legs thereof and having an exciting or variable-currentcoil '1 and a biasing or constant-current coil 22 wound around thecentral leg thereof. Device I is placed in one of the airgaps of theelectromagnet and device 2 is placed in the other airgap, both in such amanner that the magnetic field provided by the electromagnet (hwhencoils I and 22 are energized, extends in each device in a directiontransversely of the electron path between each cathode 5 and the anode 3associated therewith. Devices I and 2 are therefore placed side by side,and the electromagnet means 6 is common to the two devices.

Devices I and 2 are connected in a push-pull arrangement or as afull-wave rectifier across a source 8 of raw or unfiltered alternatingcurrent, for example the conventional 60-cycle power lines, with theexciting electromagnet coil '5 in series with the anode currents of eachmagnetron, and to this end cathode 5 of device I is connected by meansof a conductor 9 directly to one terminal of the secondary winding illof an input transformer II, while cathode 5 of device rectly to theopposite terminal of said secondary winding. Secondary winding 55 iscentertapped, and a conductor I3 connects the center tap of said windingto one end of exciting electromagnet coil "I, the other end of said coilbeing 1 connected to a point I4, from which point a pair of leads I5 andIt branch; lead I5 is connected directly to anode 3 of device I, whilelead I6 is connected directly to anode 3 of device 2.

Source 8 is connected across the primary winding ll of transformer II.

Biasing coil 22 is connected across a source 23 of direct current, forexample a battery, a choke 24 being connected in series with coil 22.

A condenser 25 is connected across battery 23,

the condenser 25 and choke 24 functioning to isolate said battery fromthe alternating voltage which tends to be induced in coil 22 as a resultof the pulsating voltage applied to exciting coil 1'. V

are connected as a single-phase full-wave rectifier across the source 8of raw or unfiltered al- A is connected by means of a conductor I2 di-1ternating current, with the exciting electromagnet coil? beingconnected effectively in series with the anode of each of the devices Iand 2.

It is apparent that the anodes of each of the magnetrons I and 2 are inseries with the coil 7, so that the coil 1 will be supplied by themagnetron anode current of each of the devices I and 2, the magnetronanode current of each of the devices therefore acting as a source ofvariable excitation for the coil 7 of the electromagnet 6 which providesthe magnetic fields for each of the magnetrons. Therefore, theadvantages explained in detail hereinabove are obtainable with thecircuit of Fig. 2, since the magnetron anode current is used to supplythe exciting coil of the magnetron electromagnet, and since themagnetrons are operated directly from m alternating current source.

Now referring to Fig. 3, a pair of magnetrons I' and 2 again are used,each magnetron including an anode 3 and a cathode 5. However, in thisfigure, each device has its own electromagnet to establish a magneticfield in the corresponding device in a direction transversely of theelectron path between the cathode and the anode thereof;

electromagnet I8 is magnetically coupled to device I while electromagnetI9 is magnetically coupled to device 2. Exciting coil 20 is wound aroundthe iron core of electromagnet I8, while exciting coil 2! is woundaround the iron core of electromagnet I9. If desired, each of theelectromagnets of Fig. 3 may be provided with a separate biasing coiland source similar to that of Fig. 2.

Cathode 5 of device I is connected, in series with electromagnet coil20, by means of lead 9, to one terminal of secondary winding I0 of input"transformer II; a cathode 5 of device 2 is connected, in series withelectromagnet coil 2|, by

means of lead I2, to the opposite terminal of sec- ;ondary winding III.

electromagnet exciting coil of each device in series in theanode-cathode circuit thereof, so that each exciting coil is supplied bythe anode current of the corresponding device, or, in other words, the

anode current of each device acts as a source of excitation for theelectromagnet which provides the magnetic field for the same magnetron.The

. advantages described in detail above are obtainable with this circuitalso, because of the series connection of the electromagnet excitingcoil and the magnetron anode-cathode circuit, with alternating currentoperation of the magnetrons.

Now referring to Fig. 4, a pair of magnetrons I and 2 havingelectromagnets I8 and I9, respectively, are again connected as afullwave rectifier across the source 8, as in Fig. 3. However, in Fig.l, the cathodes 5 of devices I and 2 are connected directly to oppositeends of secondary winding I9, while electromagnet exciting coil 20 isconnected in series between anode 3 of device I and the common lead I3from the center tap of transformer Ill, and electromagnet exciting coil2! is connected in series between anode 3 of device 2 and the commonlead I3. In this case also, each of the electromagnets may be providedwith a separate biasing coil and source similar to that of Fig. 1, if sodesired.

As in Fig. 3, the electromagnet exciting coil of access each device isconnected in series in the anodecathode circuit thereof, so that eachsuch coil is supplied by the anode current of the corresponding device;the anode current of each device therefore acts as a source ofexcitation for the electromagnet which provides the magnetic field forthe same magnetron. Therefore, the advantages described in detail aboveare obtainable with this circuit also.

Of course, it is to be understood that this invention is not limited tothe particular details as described above, as many equivalents willsuggest themselves to those skilled in the art. For example, it ispossible to use a single electromagnettype magnetron connected as ahalf-wave rectifier across an alternating current source, with theelectromagnet exciting coil in series with the anode-cathode circuit, inaccordance with the principles herein disclosed. If desired, a permanentmagnet could be used to produce the electromagnet biasing flux, ratherthan a source and coil as illustrated. Various other variations willsuggest themselves. It is accordingly desired that the appended claimsbe given a broad interpretation commensurate with the scope of thisinvention within the art.

What is claimed is:

1. An electrical circuit "comprising: an evacuated electron-dischargedevice of the magnetron type having an anode element comprising aplurality of resonant cavities, a cathode element, and an electromagnetfor establishing a magnetic field in a direction transversely of theelectron path between said cathode and said anode; means connecting saiddevice across a source of alternating current for energization solelytherefrom; and

means connecting the exciting coil of said electromagnet directly inseries between said source and one of said elements.

2. An electrical circuit comprising: a pair of evacuatedelectron-discharge devices of the magnetron type each having associatedtogether an anode element, a cathode element, and an electromagnet forestablishing a magnetic field in a direction transversely of theelectron path between each cathode and the anode associated therewith;means connecting said devices as a full-wave rectifier across a sourceof alternating current; and means connecting each electromagnet directlyin series with one of the elements associated therewith.

3. An electrical circuit comprising: a pair of evacuatedelectron-discharge devices of the magnetron type each having associatedtogether an anode element, a cathode element, and an electromagnet forestablishing a magnetic field in a direction transversely of theelectron path between each cathode and the anode associated therewith;means connecting said devices as a full-wave rectifier across a sourceof alternating current; and means connecting each electromagnet directlyin series between said source and the cathode with which saidelectromagnet is associated.

4. An electrical circuit comprising: a pair of evacuatedelectron-discharge devices of the magnetron type each having associatedtogether an anode element, a cathode element, and an electromagnet forestablishing a magnetic field in a direction transversely of theelectron path between each cathode and the anode associated therewith;means connecting said devices as a full-wave rectifier across a sourceof alternating current; and means connecting each electromagnet directlyin series between said source and the 1'0 -anode with which saidelectromagnet is associated.

5. An electrical circuit comprising: a pair of evacuatedelectron-discharge devices of the magnetron type each having associatedtogether an anode element, a cathode element, and an electromagnet forestablishing a magnetic field in a direction transversely of theelectron path between each cathode and the anode associated therewith; atransformer having a primary winding and a center-tapped secondarywinding; means connecting a source of alternating current across saidprimary winding; means connecting the anode and cathode of one of saiddevices between said center tap and one end of said secondary winding;means connecting the anode and cathode of the other of said devicesbetween said cen-. ter tap and the other end of said secondary winding;and means connecting each electromagnet directly in series between saidsecondary winding and one of the elements with which said electromagnetis associated.

6. An electrical circuit comprising: a pair of evacuatedelectron-discharge devices of the magnetron type each having associatedtogether an anode element, a cathode element, and an elec tromagnet forestablishing a magnetic field in a direction transversely of theelectron path between each cathode and the anode associated therewith; atransformer having a primary winding and a center-tapped secondarywinding; means connecting a source of alternating current across saidprimary winding; means connecting the anode and cathode of one of saiddevices between said center tap and one end of said secondary winding;means connecting the anode and cathode of the other of said devicesbetween said center tap and the other end of said secondary winding; andmeans connecting each electromagnet directly in series between saidsecondary winding and the cathode with which said electromagnet isassociated.

7. An electrical circuit comprising: a pair of evacuatedelectron-discharge devices of the magnetron type each having associatedtogether an anode element, a cathode element, and an electromagnet forestablishing a, magnetic field in a direction transversely of theelectron path between eaeh cathode and the anode associated therewith; atransformer having a primary winding and a center-tapped secondarywinding; means connecting a source of alternating current across saidprimary winding; means connecting the anode and cathode of one of saiddevices between said center tap and one end of said secondary winding;means connecting the anode and cathode of the other of said devicesbetween said center tap and the other end of said secondary winding; andmeans connecting each electromagnet directly in series between saidsecondary winding and .the anode with which said electromagnet isassociated.

8. An electrical circuit comprising: a pair of evacuatedelectron-discharge devices of the magnetron type each having associatedtogether an anode element, a cathode element, and an electromagnet forestablishing a magnetic field in a direction transversely of theelectron path between each cathode and the anode associated therewith; atransformer having a primary winding and a center-tapped secondarywinding; means connecting a source of alternating current across saidprimary winding; means connecting the anodes of both of said devices tosaid center tap; means connecting the cathode of one of said devicestoone end of said secondary winding and evacuated electron-dischargedevices of the magnetron type each having associated together an anodeelement and a cathode element; electromagnet means common to said pairof devices for establishing in each device a magnetic field in adirection transversely of the electron path between each cathode and theanode associated therewith; means connecting said devices as a full-waverectifier across a source of alternating current; and means connectingsaid electromagnet means directly in series with one of the elements ofeach of said devices.

10. An electrical circuit comprising: a pair of evacuatedelectron-discharge devices of the magnetron type each having associatedtogether an anode element and a cathode element; magnetic means commonto said pair of devices for estabiishing in each device a magnetic fieldin a direction transversely of the electron path between each cathodeand the anode associated there with; an exciting coil for energizingsaid magnetic means; means connecting said devices as a full-waverectifier across a source of alternating current; and means connectingsaid coil directly in series with one of the elements of each of saiddevices.

11. An electrical circuit comprising: a pair of 12 evacuatedelectron-discharge devices of the magnetron type each having associatedtogether an anode element and a cathode element; electromagnet meanscommon to said pair of devices for establishing in each device amagnetic field in a direction transversely of the electron path betweeneach cathode and the anode associated therewith; a transformer having aprimary Winding and a center-tapped secondary winding; means connectinga source of alternating current across said primary winding; meansconnecting the anodesof both of said devices to said center tap; meansconnecting the cathode of one of said devices to one end of saidsecondary winding and the cathode of the other of said devices to theother end of said secondary winding; and means connecting saidelectromagnet means directly in series between said secondary windingand one of the elements of each of said devices.

WILLIAM C. BROWN.

JOHN E. STACY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

